Biomechanical Evaluation of Bicortical Versus Unicortical Lag Screw Bimalleolar Ankle Fracture Fixation Techniques With Simulated Walking Boot.

PURPOSE: This study aimed to evaluate the stability of bimalleolar ankle fracture fixation techniques (bicortical and unicortical lag screw) in simulated progressive rehabilitation with a walking boot.

METHODS

Five matched pairs of lower extremities underwent simulated bimalleolar ankle fracture and were randomly assigned into these 2 repair groups. Each specimen was tested under an axial compression cyclic load test for 10000 cycles at a rate of 1 Hz while the ankle was held in 30° inclination. Radiographic assessments (screw attached lengths [length from screw head to far cortex], fracture gap, and joint clear space [medial, superior, and lateral]) by 3 examiners were performed at 0th, 5000th, and 10000th cycles. Three repeated measurements by each examiner.

RESULTS

The overall level of intra-rater reliability for all 3 raters and all measurements were found to be within "moderate" to "excellent" agreement. For radiographic screw loosening and fracture displacement, evaluation found that at no time point did either the bicortical group or the unicortical group meet the minimal threshold of clinical failure which defined as 2-mm of screw displacement or 2-mm of fracture displacement.

CONCLUSION

Both bicortical and traditional unicortical lag screw fixation techniques provide equivalent stability for medial malleolar fractures in a bimalleolar ankle fracture during simulated progressive rehabilitation with a walking boot. This could potentially have clinical benefits in patient care with earlier return to function, prevention of stiffness and loss of range of motion, and decreased muscle atrophy during the postoperative rehabilitation period.Level of Evidence: Level V: bench top testing.